This invention relates to the production of bisphenol-A. In one aspect, the invention relates to cationic exchange resins useful as catalysts for the reaction of phenol and acetone to produce bisphenol-A.
Bisphenol-A (BPA), an important base chemical used as a starting material for polyepoxide and polycarbonate resins, is commercially prepared by reacting phenol and acetone in the presence of an acidic catalyst such as sulfuric acid, hydrochloric acid or a sulfonic acid cationic exchange resin. Cationic exchange resins offer the advantage, over free acid catalysts, of safer and more convenient handling. For certain applications such as polycarbonate production, it is particularly important to produce BPA which has extremely high purity, particularly with respect to impurities which add color to the BPA. Efforts have been made to improve the quality of the BPA product and the efficiency of the BPA process by modifying the catalyst.
It is known that mercaptan compounds, used with either cationic exchange resins or free acid, are effective promoters of the phenol-acetone condensation reaction which produces BPA. When soluble mercaptans such as ethyl mercaptan are used as promoters, contamination of the product BPA with sulfur is often an undesirable side effect, necessitating additional process steps for removal and recovery of the mercaptans. The contamination problem can be alleviated by chemically bonding an amino mercaptan promoter to the exchange resin catalyst by partial neutralization or reaction of the sulfonic acid groups of the resin by the reactive group of the mercaptan containing compound.
Various mercaptan group-containing materials have been used as such chemically-bonded promoters for cationic exchange resin catalysts, including alkyl mercaptoalcohols (U.S. Pat. No. 3,049,568), C.sub.1 -C.sub.4 alkyl mercaptoamines (U.S. Pat. No. 3,394,089) and N-aminoorganomercaptan groups (U.S. 4,584,416). Since both the catalyst acidity and the presence of mercaptan groups are factors in the effectiveness of the catalyst, the one-for-one exchange of sulfonic acid sites on the ionic exchange resin for mercaptan groups represents a compromise of catalyst efficiency. It would be desirable to have ionic exchange resin catalysts for BPA production which are highly active at moderate reaction temperatures, highly selective, not subject to degradation under typical reaction conditions, and capable of producing BPA low in colored impurities.
It is therefore one object of the invention to prepare a cationic exchange resin catalyst which exhibits high activity and selectivity. It is a further object to provide a chemically-modified cationic exchange resin catalyst with enhanced stability. It is a further object to produce high quality BPA using a novel modified sulfonic acid ionic exchange resin catalyst.